A focus on JavaScript, not TypeScript. TS focus/priority is a barrier to entry in Angular 2, and it manifests in two ways.
The documentation and examples are largely TS-biased.
The architecture of Angular 2 seems to be more complex than it has to be, but it uses TS features to alleviate and justify some of that complexity. E.g things that are difficult or verbose to configure or declare in JS are more terse and straight-forward in TS, so a JS-friendly architecture is a second-class citizen.
In short, you need to know TS to use A2 effectively, and people who are happy with JS, or who are just barely wrapping their head around JS, don't want to learn what is effectively a different language. And not just a new syntax, but also the idioms and patterns that go along with that language - new patterns that you can see Angular 2 using a lot - patterns and idioms largely unfamiliar even to an experienced JS dev.
The analogy is this:
You want a new car, but to drive it, you need to relearn how to drive, rather than taking your existing driving experience and applying it to the new car. Maybe the new car isn't worth that hassle to some...